Logical partitioning (LPAR) is a mode of machine operation where multiple copies of operating systems run within a single computer system. A logical partition is a collection of machine resources that are capable of running an operating system. The resources include processors (and associated caches), main storage, and I/O devices. Partitions operate independently and are logically isolated from other partitions. In other words, each logical partition is capable of operating as if it were a separate computer system. Each logical partition can be independently reset, initially loaded with an operating system that may be different for each logical partition, and operated with different software programs using different input/output (I/O) devices. In this environment, install, initial program load (IPL), power down, and partition failures all occur without impacting other partitions on the system.
IBM Corporation began the study of logical partitioning for the S/370 architecture in 1976. The project proved that logical partitioning was a workable concept. In 1988, LPAR was first implemented on IBM's S/390 systems and has been available on IBM mainframes for more than a decade. Examples of logically partitioned computing systems are described in, for instance, U.S. Pat. No. 4,564,903, issued on Jan. 14, 1986, U.S. Pat. No. 4,843,541, issued Jun. 27, 1980, and U.S. Pat. No. 5,564,040, issued on Oct. 8, 1996.
Over that period, LPAR evolved from a predominantly physical partitioning scheme, based on hardware boundaries, to one that allows for virtual and shared resources, with load balancing capabilities. Today, all major computer manufacturers offer some form of partitioning.
The factors that have driven the evolution of mainframe partitioning over the past decade are now at work in the server system arena. Partitioning is fast becoming a necessity there also. It was estimated that during 2001, all of the major players in the server marketplace offered some degree of partitioning.
As an example, IBM's iSeries servers, and their AS/400 predecessors have offered LPAR technology since 1999 via OS/400. Logical partitioning implementation on iSeries and AS/400 servers is an adaptation of the S/390 logical partitions concept, with flexible and granular allocation of system resources. It also offers flexibility in allocating interactive performance along with high-speed internal communications between partitions.
Logical partitioning offers several advantageous features. For example, logical system partitions reduce the number of physical systems that must be managed. The benefits include easier administration through a single system console and flexibility to shift resources from one partition to another. This is a benefit as applications grow, or when demand reaches peak levels requiring additional resources. Also, workloads that cannot fully use a large system (because of contention, for example), may perform better when the workload is run as multiple images using partitions.
A partitioned system can be shared by multiple projects or departments, simplifying cost justification and cost accounting requirements. Additionally, some workloads that may not run well together on a single machine can be isolated from each other through the use of partitions. For example, there could be a general purpose interactive and batch workload composed of payroll, forecasting and planning, while another workload handles inventory control. Logical partitioning also provides an effective solution for using systems dedicated as an Internet firewall.
Also, in a scenario where some partitions on one system are backed up by partitions on a different system, logical partitioning can make fail-over situations less strenuous. A fail-over occurs when the main system encounters a problem and a backup system takes control in place of the main system. In the case of a software failure confined to a partition, only the workload of that partition shifts over to the backup partition on the second physical system. In a non-partitioned scenario, the entire system will have to fail-over.
Logical partitioning also enables customers having separate production and test environments to continue their test and developmental work without negatively impacting production work. Finally, logical partitions may be used to move an operating system or application software to updated versions. The new software can be tested in isolation before being deployed in a production environment.
One important aspect of a logically partitioned system is the management of workload running within the partitions of that system. In S/390 systems, for example, workload managers are used to manage the workload within and among the partitions. In the AS/400 and i-Series platforms, this function is performed by the hypervisor. The workload manager/hypervisor attempts to balance the workload of the partitions by moving work to the physical resources of the system.
U.S. Pat. No. 6,986,137, entitled “Method, System and Program Products for Managing Logical Processors of A Computing Environment, filed Sep. 28, 1999, provides dynamic management and adjustment of the logical processors among logical partitions in a computing environment. This dynamic adjustment is in response to the workload of the logical partition. In U.S. Pat. No. 6,986,137, the determination of whether a logical partition's resources will be adjusted is made by comparing the result of a predefined equation for the partition against one or more predefined thresholds. This resource adjustment only considers a partition's own processor utilization when determining the amount of processing units it should receive.
It is desirable to enhance the dynamic adjustment of processor resource among a plurality of logical partitions within a computing system by not only taking into consideration the processor utilization of a single partition in isolation to the rest of the partitions within the computing system, but the processor utilization of all partitions within the computing system. In this way the overall system condition of the computing system is considered so that resources assigned to one partition can be re-allocated to another partition that needs them more.